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344 lines
9.0 KiB
344 lines
9.0 KiB
// SPDX-License-Identifier: GPL-2.0-or-later |
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/* |
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* DHT11/DHT22 bit banging GPIO driver |
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* |
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* Copyright (c) Harald Geyer <[email protected]> |
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*/ |
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#include <linux/err.h> |
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#include <linux/interrupt.h> |
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#include <linux/device.h> |
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#include <linux/kernel.h> |
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#include <linux/printk.h> |
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#include <linux/slab.h> |
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#include <linux/of.h> |
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#include <linux/of_device.h> |
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#include <linux/sysfs.h> |
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#include <linux/io.h> |
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#include <linux/module.h> |
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#include <linux/platform_device.h> |
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#include <linux/wait.h> |
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#include <linux/bitops.h> |
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#include <linux/completion.h> |
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#include <linux/mutex.h> |
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#include <linux/delay.h> |
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#include <linux/gpio/consumer.h> |
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#include <linux/timekeeping.h> |
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#include <linux/iio/iio.h> |
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#define DRIVER_NAME "dht11" |
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#define DHT11_DATA_VALID_TIME 2000000000 /* 2s in ns */ |
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#define DHT11_EDGES_PREAMBLE 2 |
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#define DHT11_BITS_PER_READ 40 |
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/* |
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* Note that when reading the sensor actually 84 edges are detected, but |
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* since the last edge is not significant, we only store 83: |
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*/ |
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#define DHT11_EDGES_PER_READ (2 * DHT11_BITS_PER_READ + \ |
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DHT11_EDGES_PREAMBLE + 1) |
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/* |
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* Data transmission timing: |
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* Data bits are encoded as pulse length (high time) on the data line. |
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* 0-bit: 22-30uS -- typically 26uS (AM2302) |
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* 1-bit: 68-75uS -- typically 70uS (AM2302) |
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* The acutal timings also depend on the properties of the cable, with |
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* longer cables typically making pulses shorter. |
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* |
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* Our decoding depends on the time resolution of the system: |
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* timeres > 34uS ... don't know what a 1-tick pulse is |
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* 34uS > timeres > 30uS ... no problem (30kHz and 32kHz clocks) |
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* 30uS > timeres > 23uS ... don't know what a 2-tick pulse is |
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* timeres < 23uS ... no problem |
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* |
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* Luckily clocks in the 33-44kHz range are quite uncommon, so we can |
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* support most systems if the threshold for decoding a pulse as 1-bit |
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* is chosen carefully. If somebody really wants to support clocks around |
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* 40kHz, where this driver is most unreliable, there are two options. |
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* a) select an implementation using busy loop polling on those systems |
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* b) use the checksum to do some probabilistic decoding |
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*/ |
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#define DHT11_START_TRANSMISSION_MIN 18000 /* us */ |
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#define DHT11_START_TRANSMISSION_MAX 20000 /* us */ |
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#define DHT11_MIN_TIMERES 34000 /* ns */ |
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#define DHT11_THRESHOLD 49000 /* ns */ |
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#define DHT11_AMBIG_LOW 23000 /* ns */ |
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#define DHT11_AMBIG_HIGH 30000 /* ns */ |
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struct dht11 { |
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struct device *dev; |
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struct gpio_desc *gpiod; |
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int irq; |
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struct completion completion; |
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/* The iio sysfs interface doesn't prevent concurrent reads: */ |
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struct mutex lock; |
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s64 timestamp; |
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int temperature; |
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int humidity; |
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/* num_edges: -1 means "no transmission in progress" */ |
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int num_edges; |
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struct {s64 ts; int value; } edges[DHT11_EDGES_PER_READ]; |
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}; |
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#ifdef CONFIG_DYNAMIC_DEBUG |
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/* |
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* dht11_edges_print: show the data as actually received by the |
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* driver. |
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*/ |
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static void dht11_edges_print(struct dht11 *dht11) |
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{ |
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int i; |
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dev_dbg(dht11->dev, "%d edges detected:\n", dht11->num_edges); |
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for (i = 1; i < dht11->num_edges; ++i) { |
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dev_dbg(dht11->dev, "%d: %lld ns %s\n", i, |
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dht11->edges[i].ts - dht11->edges[i - 1].ts, |
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dht11->edges[i - 1].value ? "high" : "low"); |
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} |
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} |
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#endif /* CONFIG_DYNAMIC_DEBUG */ |
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static unsigned char dht11_decode_byte(char *bits) |
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{ |
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unsigned char ret = 0; |
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int i; |
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for (i = 0; i < 8; ++i) { |
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ret <<= 1; |
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if (bits[i]) |
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++ret; |
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} |
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return ret; |
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} |
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static int dht11_decode(struct dht11 *dht11, int offset) |
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{ |
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int i, t; |
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char bits[DHT11_BITS_PER_READ]; |
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unsigned char temp_int, temp_dec, hum_int, hum_dec, checksum; |
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for (i = 0; i < DHT11_BITS_PER_READ; ++i) { |
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t = dht11->edges[offset + 2 * i + 2].ts - |
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dht11->edges[offset + 2 * i + 1].ts; |
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if (!dht11->edges[offset + 2 * i + 1].value) { |
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dev_dbg(dht11->dev, |
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"lost synchronisation at edge %d\n", |
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offset + 2 * i + 1); |
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return -EIO; |
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} |
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bits[i] = t > DHT11_THRESHOLD; |
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} |
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hum_int = dht11_decode_byte(bits); |
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hum_dec = dht11_decode_byte(&bits[8]); |
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temp_int = dht11_decode_byte(&bits[16]); |
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temp_dec = dht11_decode_byte(&bits[24]); |
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checksum = dht11_decode_byte(&bits[32]); |
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if (((hum_int + hum_dec + temp_int + temp_dec) & 0xff) != checksum) { |
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dev_dbg(dht11->dev, "invalid checksum\n"); |
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return -EIO; |
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} |
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dht11->timestamp = ktime_get_boottime_ns(); |
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if (hum_int < 4) { /* DHT22: 100000 = (3*256+232)*100 */ |
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dht11->temperature = (((temp_int & 0x7f) << 8) + temp_dec) * |
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((temp_int & 0x80) ? -100 : 100); |
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dht11->humidity = ((hum_int << 8) + hum_dec) * 100; |
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} else if (temp_dec == 0 && hum_dec == 0) { /* DHT11 */ |
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dht11->temperature = temp_int * 1000; |
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dht11->humidity = hum_int * 1000; |
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} else { |
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dev_err(dht11->dev, |
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"Don't know how to decode data: %d %d %d %d\n", |
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hum_int, hum_dec, temp_int, temp_dec); |
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return -EIO; |
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} |
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return 0; |
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} |
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/* |
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* IRQ handler called on GPIO edges |
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*/ |
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static irqreturn_t dht11_handle_irq(int irq, void *data) |
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{ |
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struct iio_dev *iio = data; |
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struct dht11 *dht11 = iio_priv(iio); |
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if (dht11->num_edges < DHT11_EDGES_PER_READ && dht11->num_edges >= 0) { |
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dht11->edges[dht11->num_edges].ts = ktime_get_boottime_ns(); |
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dht11->edges[dht11->num_edges++].value = |
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gpiod_get_value(dht11->gpiod); |
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if (dht11->num_edges >= DHT11_EDGES_PER_READ) |
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complete(&dht11->completion); |
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} |
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return IRQ_HANDLED; |
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} |
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static int dht11_read_raw(struct iio_dev *iio_dev, |
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const struct iio_chan_spec *chan, |
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int *val, int *val2, long m) |
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{ |
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struct dht11 *dht11 = iio_priv(iio_dev); |
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int ret, timeres, offset; |
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mutex_lock(&dht11->lock); |
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if (dht11->timestamp + DHT11_DATA_VALID_TIME < ktime_get_boottime_ns()) { |
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timeres = ktime_get_resolution_ns(); |
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dev_dbg(dht11->dev, "current timeresolution: %dns\n", timeres); |
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if (timeres > DHT11_MIN_TIMERES) { |
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dev_err(dht11->dev, "timeresolution %dns too low\n", |
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timeres); |
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/* In theory a better clock could become available |
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* at some point ... and there is no error code |
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* that really fits better. |
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*/ |
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ret = -EAGAIN; |
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goto err; |
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} |
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if (timeres > DHT11_AMBIG_LOW && timeres < DHT11_AMBIG_HIGH) |
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dev_warn(dht11->dev, |
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"timeresolution: %dns - decoding ambiguous\n", |
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timeres); |
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reinit_completion(&dht11->completion); |
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dht11->num_edges = 0; |
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ret = gpiod_direction_output(dht11->gpiod, 0); |
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if (ret) |
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goto err; |
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usleep_range(DHT11_START_TRANSMISSION_MIN, |
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DHT11_START_TRANSMISSION_MAX); |
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ret = gpiod_direction_input(dht11->gpiod); |
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if (ret) |
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goto err; |
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ret = request_irq(dht11->irq, dht11_handle_irq, |
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IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING, |
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iio_dev->name, iio_dev); |
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if (ret) |
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goto err; |
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ret = wait_for_completion_killable_timeout(&dht11->completion, |
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HZ); |
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free_irq(dht11->irq, iio_dev); |
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#ifdef CONFIG_DYNAMIC_DEBUG |
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dht11_edges_print(dht11); |
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#endif |
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if (ret == 0 && dht11->num_edges < DHT11_EDGES_PER_READ - 1) { |
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dev_err(dht11->dev, "Only %d signal edges detected\n", |
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dht11->num_edges); |
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ret = -ETIMEDOUT; |
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} |
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if (ret < 0) |
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goto err; |
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offset = DHT11_EDGES_PREAMBLE + |
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dht11->num_edges - DHT11_EDGES_PER_READ; |
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for (; offset >= 0; --offset) { |
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ret = dht11_decode(dht11, offset); |
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if (!ret) |
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break; |
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} |
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if (ret) |
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goto err; |
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} |
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ret = IIO_VAL_INT; |
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if (chan->type == IIO_TEMP) |
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*val = dht11->temperature; |
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else if (chan->type == IIO_HUMIDITYRELATIVE) |
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*val = dht11->humidity; |
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else |
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ret = -EINVAL; |
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err: |
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dht11->num_edges = -1; |
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mutex_unlock(&dht11->lock); |
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return ret; |
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} |
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static const struct iio_info dht11_iio_info = { |
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.read_raw = dht11_read_raw, |
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}; |
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static const struct iio_chan_spec dht11_chan_spec[] = { |
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{ .type = IIO_TEMP, |
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.info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), }, |
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{ .type = IIO_HUMIDITYRELATIVE, |
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.info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), } |
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}; |
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static const struct of_device_id dht11_dt_ids[] = { |
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{ .compatible = "dht11", }, |
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{ } |
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}; |
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MODULE_DEVICE_TABLE(of, dht11_dt_ids); |
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static int dht11_probe(struct platform_device *pdev) |
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{ |
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struct device *dev = &pdev->dev; |
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struct dht11 *dht11; |
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struct iio_dev *iio; |
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iio = devm_iio_device_alloc(dev, sizeof(*dht11)); |
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if (!iio) { |
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dev_err(dev, "Failed to allocate IIO device\n"); |
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return -ENOMEM; |
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} |
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dht11 = iio_priv(iio); |
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dht11->dev = dev; |
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dht11->gpiod = devm_gpiod_get(dev, NULL, GPIOD_IN); |
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if (IS_ERR(dht11->gpiod)) |
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return PTR_ERR(dht11->gpiod); |
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dht11->irq = gpiod_to_irq(dht11->gpiod); |
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if (dht11->irq < 0) { |
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dev_err(dev, "GPIO %d has no interrupt\n", desc_to_gpio(dht11->gpiod)); |
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return -EINVAL; |
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} |
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dht11->timestamp = ktime_get_boottime_ns() - DHT11_DATA_VALID_TIME - 1; |
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dht11->num_edges = -1; |
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platform_set_drvdata(pdev, iio); |
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init_completion(&dht11->completion); |
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mutex_init(&dht11->lock); |
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iio->name = pdev->name; |
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iio->info = &dht11_iio_info; |
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iio->modes = INDIO_DIRECT_MODE; |
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iio->channels = dht11_chan_spec; |
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iio->num_channels = ARRAY_SIZE(dht11_chan_spec); |
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return devm_iio_device_register(dev, iio); |
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} |
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static struct platform_driver dht11_driver = { |
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.driver = { |
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.name = DRIVER_NAME, |
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.of_match_table = dht11_dt_ids, |
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}, |
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.probe = dht11_probe, |
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}; |
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module_platform_driver(dht11_driver); |
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MODULE_AUTHOR("Harald Geyer <[email protected]>"); |
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MODULE_DESCRIPTION("DHT11 humidity/temperature sensor driver"); |
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MODULE_LICENSE("GPL v2");
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